Butadiene manufacture



l l?, 1946 H. w. scHEELlNE 2,412,911

` BUTAQI'ENE MANUFAGTURE Filed July 26, 1944 ,ru-rem: -2 16 Patented Dec. 17, y1946 BUTADIENE MANUFACTURE Harold W. Scheeline, Elizabeth, N. J., assignor to Standard Oil Development Company, a cor-g` poration of Delaware Application July 26, 1944, Serial No. 546,674

(ci. 26o-eso) 5 Claims. l

This invention relates to improvements in the manufacture of butadiene and relates particularly .to improvements in the dehydrogenation of a cracked petroleum fraction knownas a cracked C4 cut to obtain butadiene with a minimum number of process steps.

The hydrocarbons normally present in a cracked C4 cut such as are obtained by the usual methods of separating cracked petroleum products into distillate or condensate fractions based on differences in boiling points, include normal butane (B. P. 31.1 F.) isobutane (B. P. 10.8 F.) n-butene-l (B. P. 20.79F.) cis-n-butene-2 (B. P. 38.7 FJ, trans-n-butene-Z (B. P. 33.8 FJ, iso-V butene (B. P. 19.8 F.), and 1,3 butadiene (B. P. 23.9 F.). The normal butenes may be readily converted to butadiene by dehydrogenation over suitable catalysts, but other C4 hydrocarbons, particularly isobutylene, are much more difficult todehydrogenate and are largely unaffected by conditions most suitable for catalytic dehydrogenation of the n-butenes. Hence, it is desirable to exclude them from the dehydrogenation treatment, as they reduce the concentration of buta- Y thereby increasing the cost of separating buta'-V diene from the dehydrogenation products' and reducing the yield by requiring additional fractionation of the products and by limiting the amount of unconverted products which can be profitably recycled. However, the boiling points of isobutene (19.8 F.) and of butene-l (20.7 F.) are so close together that the separation of these materials by distillation is extremely diiiicult and is not usually accomplished. Also, the boiling point of n-butane is intermediate between that of butene-l and the two butenes-2. Thus separation of the normal butenes from the other C4 hydrocarbons by distillation is extremely dilcult and so expensive as to be not economically practical. Only isobutane may be separated fairly readily by distillation. Separation of normal butenes by other methods involving the use of selective solvents, etc., Aalso involves a 4considerable expense, and elimination of isobutylene cann'ot normally be eifected by this means since it is so close to butene-l not only in boiling point but also in unsaturation.

The usual method of preparing the feed for the dehydrogenation step consists of fractionating to remove isobutane, most of the isobutylene and butene-l, and part of the normal butane from the feed C4 cut, and recovering a material consisting chiefly of butene-2, but containing;y

some normal butane. This material is fed to the dehydrogenation step and light gases, heavy material, and butadiene are removed from the dehydrogenation products and the remaining C4 material is recycled to the dehydrogenation step. Under this method of operation. butanes and isobutylene are usually permitted to' buildl up to about 25% of the total dehydrogenation feed stream, thus necessitating a corresponding increase in the size of the dehydrogenation equipment. In` addition, it is to be noted that separate process units are required for feed preparation for carrying out one modification of the invention and butadiene recovery.

process by which improved yields of butadiene vfrom the C4 cut are obtained.

Another object of this invention` is to provide a process in which a minimumof equipment for distillation, dehydrogenation, extraction and fractionation is required.

Other objects of the invention will be seen upon reading the following description of the invention with reference to the accompanying drawing which represents a diagrammatic illustration in partial sectional elevation of suitable equipment and indicates the flow of materials.

'I'he present invention covers a process in which the feed preparation and butadiene recovery equipment are combined. In the manufacture of butadiene by thermal or catalytic dehydrogenation of normal butene, the C4 cut which may be segregated from other dehydrogenation products contains butadiene in admixture with other hydrocarbons from which itl is not practical to separate the butadiene by simple fractionation. The C4 mixture may, however, be treated in the vapor phase with a liquid extraction agent, such as acetone, acetone plus water, furfural or furfural plus water in the presence of which the volatility of butadiene is substantially reduced with respect to the other C4 constituents so that the butadiene can be removed selectively in the solvent phase. This is sometimes referred to as extractive distillation. The extraction is simplified if cisand trans-butene-2 are removed in the solvent with the butadiene, since butene-2 in the presence of the solvent has a volatility closely approaching that of the dioleiin. After the solvent is removed, however, the butadiene and butene-2 are separable by ordinary fractionation.

Referring to the drawing, the products from the dehydrogenation unit l are passed through pipe 2 to fractionating tower 3. In the fractionating tower 3 the products are freed of C:

ln-butane and butene-l.

y mal butene available in the feed stream.

atraen hydrocarbons and lighter constituents which are 1 removed overhead through pipe 4. Cs hydrocarbons and heavier constituents are passed through pipe 5, a side cut consisting of the C4 hydrocarbon cut being removed through pipe 6 and passed extractive distillation tower l is passed by means of pipe 9 a solvent such as acetone or acetone and water. Heat is supplied, and through overy head outlet lll is passed isobutane, isobutene, The solvent with the butadiene and butene2 in solution is then passed through pipe Il into solvent stripper ,I2 where butene2 and butadiene are passed overhead through pipe I3 and the solvent free of butadiene and butene2 removed to`solvent extraction tower 1 by means of pipe 9. Butadiene and butene passing through pipe i3 into fractionating tower I4 are heated further to fractionate butadiene as an overhead product to pipe I5 and butene2 is recycled through pipe |58 to the dehydrogenation unit I.

By,the use of this process, a high yield of butadiene on butene2 can be obtained since it is unnecessary to 4discard any butene2 in order to prevent buildup in the dehydrogenation recycle circuit of isobutylene and other" materials. The stream recycled to the dehydrogenation unit willbe butene2 of highpurity, thus minimizing the size of the dehydrogenation equipment. Flnally, no separate equipment is required to fractionate the C4 feed material.

It is to be noted that butenei, despite the fact that it is a suitable feed material for dehydrogenation to butadiene, is lost from the system under this method of operation. This loss may well be approximately one-third of the nor- In addition, any butene-l formed by isomerization of butene2 during passage through the dehydroof butene-l and butanes may then be subjected to HaBOi treatment under conditions for isomerizing butene-l to butene2 and the butene2 recovered from the resulting C4 cut by the action of a selective solvent. The butene2 thus recovered may be added to the stream fed to the dehydrogenation unit. In many commercial applications. 4however, other uses exist for butene-l where isobutane and isobutylene will not have any disadvantageous effect. One example is alkylation.- In such cases, manufacture of butadiene from all or part of the available butene 2f and simultaneous manufacture of alkylate from the remainder of the butene2 and the butene-l will often be economically desirablr.

I claim:

1. Improved process for the production of butadiene'from a cracked petroleum fraction which comprises passing a petroleum fraction consisting substantially of butene2 to a catalytic dehydrogenation zone to convert the butene-Zrto butadiene, separating the dehydrogenatedproducts from the catalytic dehydrogenation zone, separating from the dehydrogenated products hy'- drocar-bonshaving three'or less carbon atoms Y tion inethe presence of a solvent having 'a preferential solvent action for butadiene and butene2 and which solvent reduces the volatility of butadiene and butene2 with respect to theother hydrocarbons other than butadiene and butene=2, separately distilling the solvent having` a prefery ential action for butadiene and containing bi1-'- tadiene and butene2 to separate the butadiene and butene2, fractionally separatingbutadiene and butene-Zand recycling the butene2 to the dehydrogenation unit.

' 2. Process according to claim l'in which 'the solvent -having a preferential solvent action for c butadiene is acetone.

3. Process according to yclaim 1 in which the solvent having a preferential solvent action for butadiene is acetone plus water. t

' 4. Process accordingto claim 1 in which the i solvent having a preferential solvent ,action for butadienel is furiural.

5. Process according jto claim 1 in which the solvent havingxa preferential solventlaction for 

